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Discussion Starter #1
I have been playing with some LED’s to replace the (easy blow) bulbs in my lighted fairing grill accents (first pic) and I have something that I like the results of for wiring. But, I am not an electrical engineer and would like a sanity check on it without getting too complicated. Since this is going on my 1800, power source will be the standard 12-14 volts. The scheme is a 1 watt 100 OHM resistor leading into 15 2 volt LED’s 5 serial and 3 parallel (second pic). Smaller OHM resistors would heat up the resistor (which I am guessing is not good). I am also trying to limit wire count behind the LED's (the main reason for 3 parallel). Another advantage of this will allow a single LED to fail without taking out others. The sanity check is to make sure that I will not have premature LED or resistor failure and still achieve maximum light within normal voltage range. The ideas here were derived from answers to questions from other people that know more about this than I. Please forgive the crude drawing, I did not have an electronics template and had to improvise and build my own resistor, LED’s, and ground point pictures. The resistor and the wiring pattern are the only things I can alter where required. I only have a test connection set up at this time, so everything I have done can be undone to satisfy change requirements.

Thanks!

LED Stats:
Category: Optoelectronics
Color: Amber/Yellow
Lens Style: round, 5mm T1 3/4
Lead Style Radial
Millicandela: 7800
Voltage: 2.0 V


Resistor Stats:
100 OHM 2% 1W110



 

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Well you need to know the ma draw for each LED. For example if the LEDs require 10ma, you have 3 parallel LEDs in a set of 5 series. Each set will draw 30ma (10X3) times the 5 sets = 150ma.

You need to drop 14volts to 10 volts so each set will have 10 volts equally dropped to 2 volts per set.

According to mister OHM to drop 4 volts at 150ma you need a 26.666 resistor rated at .6 watts.

BTW if one of the LEDs burn out the voltage across each set will change. Do the math to find out how much.

Hope this helps.
 

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Discussion Starter #4
Sanity check with LED's..... Thanks!

Thank you both for your help. That tells me what adjustments I need to make and have confidence of having it done correctly. Hopefully, I will have time to have the finished product by the end of new years day.
 

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Discussion Starter #5
Bat, I see what you mean about brightness changes with small voltage change with 5 serial. In playing with the numbers on one of the LED calculators, 3 serial and 5 parallel will have much better mA per LED prior to cranking. All of the LED’s I am using came from the same source (and part number), so they should be well matched. I bought enough LED’s to make two sets (15 LED’s x 4 strips as one set). I ended up damaging 6 of them in prior “I don’t know nothin” testing. They are not as bright as the others. I have been asking questions since then.


All of this information also makes it a little more feasible to keep LED count a little closer to bulb count. The top strip has 14 bulbs with 12 on the lower. I may end up with 15 LED on top (3 serial 5 parallel) and 12 on bottom (3 serial 4 parallel). This will allow me to still make 2 full sets without ordering replacements for the 6 dim ones. It is time to go to Fry’s and look at resistors again…….


Again, Thanks for the info!
 

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You may have a problem...

The way you are wiring this in 5 series connected sets of 3 parallel diodes at 100 ohms you will have about 120-140 ma in each branch, evenly carried by 3 routes at 40-45 ma running through each diode depending on the voltage fluctuation. That is way to much. You should look for 5 to 10 ma max for most leds. If you put to much current through them you will shorten thier life expectancy from about 85 years to days, weeks, months etc. or they will just pop, dont forget glasses.

I would personally run the voltage in parallel to each led and use 1 resistor for each even though it takes more work. A value of 2k ohms 1/4 watt, will produce 6-7ma across each led which should give you 90+ % light using most leds. This will use less than 2 watts.
 
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